Fix FastAPI middleware import error for deployment

- Removed custom BaseHTTPMiddleware that was causing import errors
- Simplified CORS configuration to use only standard FastAPI CORSMiddleware
- Kept explicit OPTIONS handler for maximum compatibility
- Fixed compatibility issue with deployed FastAPI version

main.py

@@ -1,8 +1,7 @@
 import logging
 from contextlib import asynccontextmanager
-from fastapi import FastAPI, Request, Response
+from fastapi import FastAPI, Response
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.middleware.base import BaseHTTPMiddleware
 from app.db.session import engine
 from app.db.base import Base
 from app.routers import monitors, checks, scheduler
@@ -16,33 +15,6 @@ logger = logging.getLogger(__name__)
 Base.metadata.create_all(bind=engine)
 
 
-class CORSMiddleware2(BaseHTTPMiddleware):
-    async def dispatch(self, request: Request, call_next):
-        # Handle preflight requests
-        if request.method == "OPTIONS":
-            response = Response()
-            response.headers["Access-Control-Allow-Origin"] = "*"
-            response.headers["Access-Control-Allow-Methods"] = (
-                "GET, POST, PUT, DELETE, OPTIONS"
-            )
-            response.headers["Access-Control-Allow-Headers"] = "*"
-            response.headers["Access-Control-Max-Age"] = "3600"
-            return response
-
-        # Process the request
-        response = await call_next(request)
-
-        # Add CORS headers to the response
-        response.headers["Access-Control-Allow-Origin"] = "*"
-        response.headers["Access-Control-Allow-Methods"] = (
-            "GET, POST, PUT, DELETE, OPTIONS"
-        )
-        response.headers["Access-Control-Allow-Headers"] = "*"
-        response.headers["Access-Control-Expose-Headers"] = "*"
-
-        return response
-
-
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     # Startup
@@ -62,10 +34,7 @@ app = FastAPI(
     lifespan=lifespan,
 )
 
-# Add custom CORS middleware
-app.add_middleware(CORSMiddleware2)
-
-# Also add the standard CORS middleware as backup
+# Add CORS middleware
 app.add_middleware(
     CORSMiddleware,
     allow_origins=["*"],
@@ -98,8 +67,6 @@ async def health_check():
 @app.options("/{full_path:path}")
 async def options_handler(full_path: str):
     """Handle preflight OPTIONS requests"""
-    from fastapi import Response
-
     response = Response()
     response.headers["Access-Control-Allow-Origin"] = "*"
     response.headers["Access-Control-Allow-Methods"] = "GET, POST, PUT, DELETE, OPTIONS"